I was thinking about that, too, BertieBotts! Tantrummers must not be allowed to win, of course!
I still think human nature in most cases will enforce a "stop" in many cases. However, for the children in the dance classes, and the law firms faced with the unqualified (and unqualifiable) paralegal, that "stop" can be enforced from above.
Also, I do believe that children and adults can cope with increasingly sophisticated ideas in life, so learning when and how to give up is a lesson which doesn't necessarily undermine "don't give up". Also, I'd like to repeat what I said about achievable goals. In childhood, parents and teachers should be setting achievable goals, so children have a taste of achievement.
Scientific method might be a particularly good way of learning to defer success, try different things without feeling that one failure is total failure. It's a real shame, therefore, that science teaching in schools has fallen off so greatly...